THE O'Farrell government's WestConnex road project faces mounting criticism because it does not actually go to Port Botany, despite being sold as a solution to the congestion in the area.

The criticism is expected to mirror that levelled at motorways planned under Labor, which were advertised as making it easier for trucks to get to and from the port even though they did not enter Botany.

Infrastructure NSW, the organisation that drew up the plan for WestConnex, says it looked at the idea of suggesting a motorway deep into the port area, but decided against it because of cost factors.

The difficulty of providing new ways for trucks to access Port Botany, through which 2 million containers move every year, has long troubled road planners drawing up new proposed motorways for Sydney.

In early 2011, for instance, Sydney Ports was asked if it thought there was much point in building a new M5 motorway to Sydney's south-west that did not provide a direct link to Botany.

It said there was not.

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''Sydney Ports considers it essential that any proposal to extend the M5 East should ensure that additional capacity is provided directly to Port Botany,'' the Ports Corporation wrote in response to a query from Infrastructure Australia, which advises the federal government.

''The current proposal would not achieve this,'' it said in relation to the plan under development by the Keneally Labor government.

Two years on, the O'Farrell government's WestConnex is the latest plan for a motorway in the area. And one of its stated aims was to help the city's economy by making it easier for trucks to get in and out of the port.

''The freeing up of Botany, when you have 100,000 people a day coming out of aeroplanes, when you have container movements that are going to triple in size, understanding that and how that might be freed … has driven how we think,'' the chief executive of Infrastructure NSW, Paul Broad, said when announcing the project in October.

But the closest WestConnex goes to Port Botany is about 8 kilometres from the port, at the point where it veers north through Arncliffe on the western side of Sydney Airport.

Early and unreleased plans for WestConnex featured a direct corridor for trucks to get to and from the port and on to the new motorway.

But a spokeswoman for Infrastructure NSW said the organisation looked at the idea but decided against it.

She said: ''When assessing the value for money of a dedicated road link, we considered a number of issues, including the need for WestConnex to address a wide range of road transport markets and capacity projections (for example, current and projected traffic is far greater to Sydney Airport than Port Botany) and the government's policy to increase rail mode share from Port Botany.

''Our analysis showed the capital cost of a dedicated road link to Port Botany around or under the airport would be extremely high and would not provide the best value to meet the forecast freight task. Accordingly we looked at better value alternatives.''

These include a truck layover around Foreshore Road, widening Mill Pond Road between General Holmes Drive and Botany Road, and making Bourke Road and O'Riordan Street one way each.

But the absence of a link road potentially cruels the chance of WestConnex winning support from Infrastructure Australia, which has lashed out at previous motorway proposals that did not link to Port Botany.